Magnetic disk devices include a read/write channel, head amplifier IC, and the like. In recent years, magnetic disk devices have a function to change a current value of a data pattern of a write current corresponding to a data pattern of write data. This function is referred to, for example, data dependent write (DDW), or pattern dependent write (PDW), or the like. The magnetic disk device inputs a control signal from the read/write channel to the head amplifier IC to change a current value of the data pattern of the write current, and on the basis of the control signal, changes the current value of the data pattern in the head amplifier IC to input the write current with the changed current value to a head. The magnetic disk device changes a current value of a data pattern of a high frequency write current and a current value of a data pattern of a low frequency write current, respectively, for outputting a suitable write current to the head. In that case, the magnetic disk device needs to input a control signal used for changing the current value of high frequency data pattern and the current value of low frequency data pattern from the read/write channel to the head amplifier IC. Since the magnetic disk device recognizes the high frequency data pattern or the low frequency data pattern in the read/write channel, require terminals, lines, and the like to transmit/receive the control signal between the read/write channel and the head amplifier IC.